Motorway Speed Limits

[#1]

Plans here in Wales for those fifty mile per hour speed limits on the M4 to be made permanant.

Great idea, but given it's only on a few sections the limit is more often than not ignored despite those ANPR cameras. Far better in my opinion to introduce such a limit as you enter Wales. No ifs, not buts... no seventy miles per hour anywhere. Give it a few years and during the last gasp of the internal combustion engine, all will be reduced to this limit I reckon and not before time.

Want to go more than fifty? Then go electric. 

[#2]

@Minivanman Seems like we both had the same idea so seeing as Mav prefers yours i will add mine here!                                                 I see that some stretches of the M4 and also some A roads are to have a permanant 50mph speed limit 50mph to cut down on emisions. Dont know if this is a good idea. My cars gear change from 5th to 6th is at 50mph so most of the time the engine would be running at higher revs producing more emisions than if i was driving at say 55mph in 6th. Any thoughts I could be wrong.

[#3]

No preference - I go for the earliest post or the one with the most replies.

On reflection I should have merged these threads

[#4]

---

@TTman wrote:

                                              I see that some stretches of the M4 and also some A roads are to have a permanant 50mph speed limit 50mph to cut down on emisions. Dont know if this is a good idea.

---

That is a bit weird.... how can driving slower, cut emissions ? 

Say it takes 15 minutes to travel through a section at 70mph....  with emissions at minimum because the theory is, that the car`s own inertia, will be "assisting" it`s forward motion, therefore, the amount of fuel required to maintain that speed will be less.

Now.. impose a 50mph speed limit... and the time taken to travel through that same section will be increased.  say 20 minutes..  For the purpose of this argument.

The car`s own inertia is less, and therefore the driver will be in a lower level of gear, ( even worse on automatic gearbox vehicles). therefore using more fuel, and issuing more "emissions"... add to that scenario, those increased "emissions" will be added to, because of the journey time being increased due to the lower speed to traverse the section...

summing up... lower speed, equals an increase in the "emissions" not a lessening..

[#5]

Especially if you end up with a bottleneck effect the 50mph limit will most likely cause.

[#6]

Well I'm confident that those that know about such things and having decided to reduce speeds know what they are talking about. 

Makes sense to me from a laymans perspective that less energy from a petrol or diesel engine means less pollution and besides, why on earth make cars that go so fast. My old 2CV would get me from A to B in much the same way as Joe Bloggs in his four litre beast. You'd be surprised how often I'd catch up with them at some point in the journey in much the same way as I do now with my 1.2 Fiesta.

Here's a novel idea make the engines smaller, along with those egos.  

[#7]

---

@Minivanman wrote:

Well I'm confident that those that know about such things and having decided to reduce speeds know what they are talking about. 

I'm not!

It's just another way to try to catch people speeding on a road that was built to take traffic at 70mph.

[#8]

@Minivanman More that the politicians are seen to be doing something. Whether it does or not remains to be seen. If not they will probably fiddle the figures to give them the answer they want

[#9]

Well that's the cynic in all of us talking @Mav but in pondering the subject and having looked at a couple of sites, all agree with research to back it up that reduced speed reduces emmisions. No accounting for how people drive which is the only fly in the ointment - but there you have it.

Happy to link in what I have found but all of us here can find others I guess,

[#10]

@TTman 

Sorry we crossed posts, it happens.  

As for those politicans being on the fiddle, you may well be right!

[#11]

I understand how driving faster causes more pollution due to more energy having to be used to overcome friction, wind resistance etc., but as pollution increases whilst a vehicle is accelerating, IMO it follows that one of the biggest causes of vehicles slowing then accelerating is those stupid speed restrictions in the form of humps everywhere.

Isn't one of the purposes of Smart Motorways to enable smoother flow of traffic, thereby cutting down on pollution by eliminating much of the repeated accelerating required in stop-go traffic?  I don't know whether those particular stretches of the M4 in Wales are Smart, but if not they seem to be classic candidates for conversion, then at least the limit could be raised to 70 at times of lighter traffic.

[#12]

It doesn’t work the way you think @shutter. If your car does 50MPG at 50MPH you’ll be able to travel 50 Miles in 1 Hour using 1 Gallon of fuel. However travelling at 70MPH you can do the same distance in about 43 minutes but use more fuel so more emissions. So the assumption is if you take a bit more time on your journey you'll be able to lower your emissions.

[#13]

That particular stetch @RobPN is one that I used to know well and it's been a real pain ever since it was opended.

It cuts alogside the edge of Port Talbot which meant of course the town wanted access so two (or it might be three now) slip roads join without a lot a space or time to spare... so the traffic is obliged to slow down which it failed to do and which is why as traffic increased over the years, they imposed a 50mph limit. Nothing to do with pollution, all to do with road safety. 

The odd thing is that stretch also runs besides the steel works which was the worst in the UK for particle matter pollution.

The bottom line I suppose is for us all to drive slower and for us all in doing so to reduce pollution and quite honestly, whether it does or not - especially around Port Talbot.

Welcome to south Wales cough cough. 

[#14]

@Minivanman 

Is that a recent photograph ?

Looks grim !

[#15]

@gleneagles 

That's when it was being built but trust me, it's still as grim.